Group delay measurements are performed by a measurement device that is connected to a device under test in order to test its characteristics with regard to group delay behavior of a signal passing through said device under test. In general, the group delay relates to the delay of the amplitude envelopes of the signal transmitted, in particular a narrowband signal, wherein the group delay to be measured is caused by the device under test itself. Typically, the group delay, also called group delay time or time delay, occurs when the device under test is excited with a high frequency signal, for example a radio frequency signal. The occurring group delay time can be obtained from the rate of change of phase dependent upon the rate of change of frequency.
Typically, a network analyzer, for instance a vector network analyzer (VNA), is used as measurement device. Generally, the linear transmission behavior of the device under test has to be determined for different fields of application.
In the state of the art, the methods for group delay measurement are performed with a two-tone stimulus signal that is applied to the device under test as described in U.S. Pat. No. 8,983,796 B2, for instance. Since the time delay is different for various frequencies provided the device under test is not phase linear, two tones having different frequencies are used for determining the group delay behavior, in particular the phase linearity. Accordingly, a delay variation of both signals occurs as these signals are not delayed by the same amount of time. However, this method of measuring the group delay requires the usage of a combiner or to reconfigure the test setup in order to use a coupler as a combiner.
The methods known in the prior art require two different sources for providing the two-tone signal such that two ports of the measurement device are occupied for the purpose of measuring the group delay. Thus, these two ports required for the measurement cannot be used for any other measurement. Accordingly, the usability of the measurement device is limited. Furthermore, an external combiner or one of the couplers has to be used in order to combine the signals of both sources.